Question

A and B can do a piece of work in 10 days, B and C in 15

days and C and A in 20 days, C alone can do the work in :

Answer 1

Answer 24 hours
(A + B)’s 1 day’s work 
(B + C)’s 1 day’s work 
(C + A)’s 1 day’s work 
On adding,
2(A + B + C)’s 1 day’s work 
∴ (A + B + C)’s 1 day’s work 
∴ A’s 1 day’s work 
∴ A alone will complete the work in 24 days.